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Abu Sa'id Ahmed ibn Mohammed ibn Abd al-Jalil al-Sijzi (short for al-Sijistani) was a Persian astronomer and mathematician from Sistan.

Sijistan or Sistan is a region in the east of current Iran. Its historical name is Sakastan from the name Saka who were East Iranian inhabitants of the region. Sakastan is mentioned in abundance in the Shahnama.

Al-Sijzi is thought to have been born around 945 CE, and lived through about 1020. His main scientific focus was astronomy. He had a deep knowledge of literature which he used to his advantage. He dedicated work to 'Adud al-Daula and the prince of Balkh. He also worked in Shiraz making astronomical observations from 969-970. He also did a lot of geometry work.



Al-Biruni wrote that al-Sijzi believed in a heliocentric system in which the Earth was moving and that he invented an astrolabe called the "Zuraqi" based on this idea:[1]

"I have seen the astrolabe called Zuraqi invented by Abu Sa'id Sijzi. I liked it very much and praised him a great deal, as it is based on the idea entertained by some to the effect that the motion we see is due to the Earth's movement and not to that of the sky. By my life, it is a problem difficult of solution and refutation. [...] For it is the same whether you take it that the Earth is in motion or the sky. For, in both cases, it does not affect the Astronomical Science. It is just for the physicist to see if it is possible to refute it."


Sijzi was a mathematician who made a special study of the intersections of conic sections and circles. He replaced the old kinematical trisection of an angle by a purely geometric solution (intersection of a circle and an equilateral hyperbola.)


  1. ^ Seyyed Hossein Nasr (1993), An Introduction to Islamic Cosmological Doctrines, p. 135-136. State University of New York Press, ISBN 0791415163.


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